Summary: The Secretory Mechanisms and Dysfunction Section investigates the molecular nature and function of the ion transport mechanisms involved in the fluid and electrolyte secretion process in the exocrine salivary gland. We are probing the structure-function relationships of cotransporter, exchanger and channel proteins using a combination of RNA-seq, molecular biology, gene modification, proteomics and functional studies in mouse and human salivary glands. Accomplishments/conclusions: Cation-dependent Anion Exchanger Ae4 (Slc4a9): Genetic disruption and functional studies reveal that Ae4 (Slc4a9) is a non-selective, cation-dependent anion exchanger. Ae4 (Slc4a9) supports salivary gland secretion through -adrenergic receptor activation of cAMP signaling. Solute carrier family 26 (SLC26) member 6 (SLC26A6 or CFEX/PAT-1): RNA sequencing-based transcriptional profiling and Western blots revealed that Slc26a6 is highly expressed in mouse submandibular and sublingual salivary glands. Slc26a6 is located at the apical membrane of submandibular salivary gland acinar cells, where it mediates Cl-/oxalate exchange and plays a critical role in the secretion of oxalate into saliva. Transcriptional Profiling of the Three Major Salivary Glands of the Adult Mouse: RNA-Seq was used to better understand the molecular nature of the biological differences among the three major exocrine salivary glands in mammals. Transcriptional profiling found that the adult salivary glands express greater than 14,300 protein-coding genes. Moreover, transcriptional profiling identified a limited number of highly expressed genes, differentially expressed genes, and unique transcription factors that represent the transcriptional signatures underlying gland-specific biological properties. Salivary Glands of Eda null X-LHED Mice: Mutations in the ectodysplasin A gene (EDA) cause X-LHED (X-linked hypohidrotic ectodermal dysplasia), the most common human form of ectodermal dysplasia. Fluid secretion was intact in the salivary glands of Eda-deficient mice but displayed marked Na+ and Cl- reabsorption defects that correlated with the loss of duct cells and decreased Scnn1 Na+ channel expression. These results provide a likely mechanism for the elevated NaCl concentration observed in the saliva of affected male and female patients with X-LHED. Na+-HCO3- Cotransporter Slc4a7 (NBCn1): The HCO3- secretion mechanism in the exocrine salivary gland is unclear but is thought to be driven in duct cells by the coordinated activity of multiple ion transport proteins including members of the Slc4 family of bicarbonate transporters. Our results reveal that Slc4a7 targets to the apical membrane of mouse submandibular gland duct cells. However, functional studies using Slc4a7-/- mice suggest that Slc4a7 contributes little if any to intracellular pH regulation or stimulated HCO3- secretion.